Determination of mass transfer coefficients in high-pressure two-phase flows in capillaries using Raman spectroscopy

Abstract

Mass transfer of COi into a H20 rich phase at high pressure in a capillary is studied • A rnethod for the determination of volumetric mass transfer coef ficient is presented.• A thermodynami c model and Raman spectroscopy are cou pied to obtain C(h con centrations.• The influen ce of flow rates on the volumetric mass transfer coefficient is studied.• The mass transfer coefficient varies along the length of the micro capillary tube.

Determination of mass transfer coefficients in high-pressure CO2-H2O flows in microcapillaries using a colorimetric method

“…Firstly, it can be seen that k L a L is not constant along the microreactor; depending on the operating conditions, the volumetric mass transfer coefficient is 5-15 times higher close to the bubble generation zone compared with at the end of the tube. This is similar to what was found by (Deleau et al, 2020;Tan et al, 2012;Abolhasani et al, 2015) for various gas-liquid systems at both high and ambient pressure. Using the measured values of a L obtained via image analysis, it is possible to deduce the value of k L at different positions along the capillary tube to better understand why k L a L is higher in the bubble generation zone.…”

“…order of magnitude is similar to that obtained for the same system using the Raman spectroscopy method (0.2 s À1 to 4 s À1 ) described by Deleau et al (2020). This difference between the results is, at least in part, due to the slightly larger capillary diameter (300 mm) employed in Deleau et al (2020) compared with 250 mm capillary tube diameter used in this study. Indeed, the mass transfer characteristic time, which is proportional to the square of the diameter, is 1.4 times higher with a diameter of 250 mm compared with that obtained in a capillary tub with a diameter of 300 mm.…”

“…Decoupling of the specific surface aL and the local mass transfer coefficient kL effects on the volumetric mass transfer coefficient kLaL. order of magnitude is similar to that obtained for the same system using the Raman spectroscopy method (0.2 s À1 to 4 s À1 ) described by Deleau et al (2020). This difference between the results is, at least in part, due to the slightly larger capillary diameter (300 mm) employed in Deleau et al (2020) compared with 250 mm capillary tube diameter used in this study.…”

“…The CO 2 concentrations obtained in this work correspond to discrete values due to the use of experimental data from Peng et al (2013). In order to obtain concentration curves, which are required to calculate the first derivative of the concentration for the determination of the volumetric mass transfer coefficient, the CO 2 concentration values along the microchannel are filtered with a fast Fourier transform (FFT) algorithm as presented in our previous work (Deleau et al, 2020). The normalized concentration profiles obtained with the FFT algorithm are then used to compute the first derivative of CO 2 concentrations, dC CO 2 dz .…”

“…Hence for high-pressure systems where there is significant mass transfer of species between phases, other measurement methods are required. Recently, Deleau et al (2020) have presented a method for the experimental determination of local volumetric mass transfer coefficients k L a L in a high-pressure (up to 10 MPa) two-phase flow of H 2 O and CO 2 in a microcapillary. This method combines a thermodynamic model and Raman spectroscopy measurements to obtain CO 2 concentrations, which are used to calculate local k L a L values.…”